You can do this by double clicking on the instrument you wish to trade which will open up the Order window or you click on any other instrument and the select the instrument you wish to trade in the Order window.
Once you have selected the volume you want to trade, you can either Buy or Sell that instrument by clicking on the corresponding button at the bottom of the window.
You can also place a new order by clicking on the New Order button in the toolbar and then selecting the instrument you wish to trade from the drop down list.
Enabling One Click Trading
If you prefer One Click Trading feature, right click anywhere in the Chart window, and enable One Click Trading.
This should place the order tool in the upper left corner of the Chart window.